There was a story by Nate Hoekstra in the Grand Valley Magazine spring 2017 about bluegill sex. It is well known that male bluegill sunfish fight off other males from their nests and fight for breeding. “But variety in the species’ gene pool may rest on the backs of smaller, sneakier and more clever males who have a variety of tricks up their gills to keep their genetic lineage alive against tough odds.”
The article discussed how the smaller, more clever fish out-compete the bigger, stronger males in a breeding population. Here is the nitty-gritty:
Bluegills have 2 paths to maturity. One leads the fish to behave in a traditional parental male model. They sexually mature at about 7 years old. The other male path leads to alternative reproductive habits. When they sexually mature at 2 years old they’re called “sneakers” and they "use their small size and quickness to dart in and out of nests that are occupied by a parental male and a spawning female, and can beat the male to the eggs, sneaking their way to a successful fertilization”.
As the sneakers age they use another trick to reproduce. They transform into “satellite” males that look like females in size, coloration and behavior traits. "This camouflage act allows satellite males to camp in nests with parental males—completely undetected—until another female comes to spawn, and the satellite will attempt to fertilize the eggs instead of the parental male.”
In studying the brains from each group of fish researchers have discovered the sneaker males showed a higher level of gene expression differentiation, which is important for increased spatial working memory. This gives them enhanced capacity for spatial awareness – “a great skill for a fish whose success at reproduction is based on his ability to sneak in and out of small, tight spaces very quickly.”
Who knew fish reproduction could be so surprisingly complex?!